1. Field of the Invention
The agricultural sprayer for applying liquid herbicides, insecticides, and fertilizers to farm fields and crops growing in farm fields, includes a spray boom with a center section, a left wing and a right wing mounted on the front of a trailer with a hitch adapted to be connected to a tractor.
2. Prior Art
Agricultural sprayers are available that are mounted on a tractor as well as sprayers that are mounted on a trailer. The tractor mounted sprayers can include a tractor that is designed specifically for application of liquids. Such tractors are high clearance units that are generally not suitable for tillage or harvesting operations. Such tractors and integral sprayer units can spray a number of acres per hour. When tractors with integral sprayer units are not needed for spraying, they are idle. A farm must be relatively large to justify such a sprayer.
Tractor mounted sprayer attachments that mount directly on a tractor are also available. The tractors that carry such sprayer attachments are also useable for tillage or harvesting operations, when a portion or all of the sprayer attachment is removed. These units require time to convert to and from spray units. During the conversion they are not useable for spraying or any other function. They are out of commission. During use as sprayer units, they are less maneuverable than tractors with integral sprayers that are used for spraying only. They are also heavier then dedicated sprayer tractors and cause more soil compaction. Due to their increased weight, sprayer attachments mounted on conventional farm tractors also require more fuel per hour than an integral sprayer unit with the same capacity sprayer.
Trailer mounted sprayers include a trailer frame supported by two or more wheels journaled on one or more axles. A hitch assembly on the front of the trailer is adapted for connection to the draw bar of the tractor. A tank is mounted on the frame. A sprayer boom is mounted on the trailer frame. Pipes, with a plurality of spaced apart nozzles, are mounted on the sprayer boom. A pump and liquid metering valve is connected to the tank and to the pipes. The pump is driven by the tractor through a power take off shaft or through a hydraulic motor. Farm tractors used today in North America have power take off drive shafts that can drive a shaft connected to the sprayer pump as well as an internal hydraulic pump that can supply hydraulic fluid under pressure to a remote hydraulic motor connected to a sprayer pump mounted on the trailer frame.
The sprayer boom may spray a strip that is sixty (60) or more feet wide during each pass through a field. The boom, to spray such a strip, may include a short center boom section, a left wing assembly and a right wing assembly. Each wing assembly includes an inner wing section pivotally attached to the trailer frame and one or more outer wings pivotally attached to the inner wing section. Hydraulic cylinders are provided for folding both wing assemblies to a transport position. A boom vertical lift assembly permits the elevation of the nozzles to be adjusted to a position between about eighteen inches (18″) above the ground and a position about fifty inches (50″) above the ground. A self-leveling assembly of some type permits one trailer wheel to move up over a rock and down and across a furrow without moving outer ends of the boom vertically a significant distance.
A center boom section as well as the left and right wing assemblies are mounted on the rear of the trailer-frame on some sprayers. In this position to the rear of the trailer axle, movement of the trailer wheels up and over a six inch (6″) high ridge will pivot the trailer about the connection to the tractor and raise the boom upward more than six inches (6″). Movement of both trailer wheels across a six inch (6″) deep furrow will lower the boom more then six inches (6″). Vertical movement of the tractor will also move the boom at the rear of the trailer in the opposite direction from the vertical movement of the tractor rear wheels. Vertical movement of the boom places large forces on the sprayer boom and the trailer frame and makes it necessary to reduce tractor speed if the field to be sprayed is rough. Reduction of tractor speed reduces productivity, thereby increasing the per acre cost of spraying.
The left wing assembly and the right wing assembly on some trailer sprayers have been moved forward to a position near the front of the liquid storage tank. In the forward position, both wing assemblies are midway between the tractor rear wheels and the trailer wheels. In this position, passage of the trailer wheels up over a six inch (6″) ridge will raise the boom only about 3 inches (3″). Passage of the trailer wheels across a six inch (6″) deep furrow will lower the boom assemblies about 3 inches (3″). Movement of the tractor rear wheels vertically will also move the boom wing assemblies about half the vertical distance moved by the tractor wheels. Mounting the boom wing assemblies forward of the liquid storage tank reduces vertical wing assembly movement, thereby substantially reducing loads on wing booms and the trailer frame. Some manufacturers of trailer mounted sprayers have moved the wing assemblies forward while leaving the boom center section at the rear of the trailer. They could not move the boom center section forward because the trailer frame interferes with vertical boom adjustment. This arrangement works reasonably well on relatively flat fields. A field that has terraces generally requires the tractor to move in an arcuate path parallel to the terrace. When following an arcuate path, the center boom on the rear of the trailer will overlap one wing boom nozzle and leave an untreated strip between the other wing boom nozzle and the center boom. The overlapping spray may provide excessive spray and damage crops. The missed strip may, for example, leave a narrow strip of weeds that are not killed by an herbicide. A few weeds that go to seed can result in seeding most of a field. A few insects that escape an insecticide can damage an entire crop.